At higher rounds, you can even create clusters of crawlers (zombies with destroyed legs due to which the crawl) by throwing in a frag grenade in the jumbled zombies as a result of the looping. Crawlers are very slow and easily avoidable, and can be finished off with a badass RPD (if the Mystery Box was nice to you) or even an RPG.
A couple of great finds here in the two-story barn. Firstly you’ll find a Perk-a-Cola and secondly there is a zombie-clearing wall-weapon hidden behind a stack of crates.
Your trips to the Mystery Box will also be more difficult now, and the only real way to make one without incident is to create crawlers.
The Farmhouse is the second location of the Mystery Box, which you can find on the second floor. Besides that you can also drop down from the balcony (Stack of boxes) and reach the outside grounds. A pretty nifty escape route in the event your exit is cut off by a swarm of the undead.
The Farm is probably the smaller of the Green Run Survival maps, and is also the harshest. It’ll start you off in the complete open, facing a truck.
After round 5 and onwards, it’ll be time for you to go crazy. Drink a Jugger-Nog and go into the open – standing in the barn and house the whole time won’t get you anywhere now, as the zombies will be pouring through the fog.
Another essential part of the map is a largish house located to the right of the truck. It can be considered as the center of the map, but requires you to unlock the house for 750 credits. The top balcony of the house is where you’ll find the mystery box. There is also a Perk machine there.
To make matters worse, the fire-lava on the floor is scattered everywhere, and it’s quite easy to actually step on it and set yourself ablaze for a bit.
At higher levels, looping around the truck becomes very difficult with faster and angrier zombies. In this stage you want to get Double Tap (located on the upper story of the barn) and increase the radius of your loop, while being a little more careful. Avoid the fire at this stage, and DO NOT cramp up into a corner during your loop, or you will be dead for sure.
Check out this Black Ops 2 Zombies Farm Survival Strategy Guide to learn how to survive waves after waves of zombies on this map.